Medical treatments inside a blood vessel using a highly-functional catheter such as a balloon catheter, stent or the like are generally known. Whether for the diagnosis before the surgical-operation thereof or for the progress confirmation after the surgical-operation, it has become popular to use an imaging apparatus for diagnosis such as an optical coherent tomographic diagnosis (OCT: Optical Coherence Tomography) apparatus or the like.
The imaging apparatus for diagnosis includes a catheter installed with an optical fiber on the distal end of which an optical lens and an optical mirror are mounted. The imaging apparatus is configured such that the catheter is inserted inside a blood vessel of a patient, light is illuminated onto the blood vessel wall via a rotatable optical mirror, a radial scan is carried out by light-receiving the reflected light from the blood vessel via the optical mirror and thereafter, a cross-sectional image of the blood vessel is constructed based on the reflected light that is obtained. In addition, an improved type of OCT has been developed as an optical coherent tomographic diagnostic apparatus utilizing wavelength sweep (SS-OCT Apparatus: Swept-source Optical coherence Tomography Apparatus).
According to the basic principle of the optical coherent tomographic diagnostic apparatus, light outputted from a light source inside the apparatus is divided into a measurement light and a reference light, and the measurement light is emanated toward an optical mirror of an optical fiber inside the above-mentioned catheter. Then, scattered light reflected by a biological tissue is light-received via the same optical fiber, an interference light is obtained with respect to reference light reflected by way of a predetermined distance, and a tomographic image of a biological tissue (blood vessel) in the vicinity of the catheter is obtained based on the intensity of the interference light (for example, see U.S. Pat. No. 7,738,941).
However, a blood cell component such as a red blood cell or the like is present inside the blood vessel. Light reflection thus occurs on the surface of the blood cell component and hinders obtaining an aimed highly accurate tomographic image of the blood vessel. Consequently, in order to exclude the blood cell component, it is known to temporarily create a state in which no blood cell component exists by discharging liquid such as a physiological salt solution, a contrast agent or the like inside the blood vessel. Emanation of the light and light-receiving of the reflected light is then carried out while the blood vessel is in this temporary state. The operation of discharging the liquid into the blood vessel is referred to generally as a flush operation and the liquid discharged at that time is referred to as flush liquid.
For the flush liquid, there are several types provided corresponding to the use purposes thereof. Specifically, as explained previously, these are a contrast agent, a physiological salt solution, and a mixed liquid thereof in which the mixing ratio thereof is different.
A problem arises, however, that the refractive index of the light is different depending on the type of the flush liquid. As well known in the past, the light speed propagating inside a medium is dependent on the refractive index which that medium possesses. Therefore, when the apparatus is set up with a flush liquid which is different from the flush liquid actually used, a phenomenon occurs in which the obtained scale of the tomographic image of the blood vessel is different from the actual scale.
Generally, when the flush liquid to be used is determined, before the flush operation, an image of the boundary surface between the catheter and the blood is created and displayed by rotating the optical mirror inside the catheter. Then, the refractive index of the utilized flush liquid is made a parameter and while the optical path length of the reference light is adjusted, an operation is carried out (generally, referred to as calibration operation) which makes the image (having an approximately round shape) on the boundary surface thereof coincide with a circle (land mark) which becomes a preset reference. Thereafter, a flush operation is actually carried out and the optical mirror rotating inside the catheter is moved at a constant speed along the axis of the blood vessel. The movement of the rotating optical mirror corresponds also to a pull-back operation of the rotating optical fiber, so that it is generally referred to as a “pull-back operation”. In addition, the series of operation for obtaining the image is called as “imaging operation”.
If for some reason, after the calibration operation is carried out, the type of flush liquid being used must be changed or if the refractive index of the flush liquid, which was set when carrying out the calibration operation, has been set erroneously, naturally, it is then necessary to carry out the calibration operation again after changing the refractive index of the flush liquid to a correct one. This is because there is a possibility, in the diagnosis of a blood vessel before a surgical-operation of arranging and indwelling a stent at a blood vessel, that the diagnosis is flawed when there is an error in the scale and there could occur a situation in which a stent having an erroneous size might be determined.
Further, in a case where it is recognized that there was an error in the setting of the set flush liquid after carrying out the flush operation and the pull-back operation, the operations subsequent to the calibration operation must be carried out again and thus occurs a situation in which the surgical-operation time period and the number of surgical-operations will increase, and the stress thereof will be exerted on the patient.